The major problem that most people have is that 20% of their study time is effective in increasing their score -- and the rest is wasted as they go through the motions of practice problems and studying concepts. The problem gets even worse when you've had a significant study gap and can't just pickup and restart where you left off.
Here's what I can see about your stage of prep:
1) You're now in the zone of taking your score from good (top 25%) to elite (top 6%). The previous jumps you made could be driven by the standard study process (concept driven and revolving around practice problems). But this next jump is all about Test Taking Skills
2) You're probably running low of unused practice tests -- so you have to maximize the ones you have.
3) You're wondering if more of the same study pattern is going pay off. (answer is NO by the way).
Your last month of prep has to be precise and, by extension, efficient. You can't afford 20% time efficiency.
The key to achieving that is answering the WHY question really precisely: WHY did my last test put me at the 670 level? What were my precise Test Taking Skill (reasoning method) gaps, in quant and verbal.
Figuring this out needs two things -- a live IN-TEST assessment and ideally an expert assessing your approach. Those two things will give you the 80% efficiency and score jump you want in 1 month.